Many forms of device have been proposed for dispensing fluids, for example medicaments, as sprays of fine droplets or aerosols. In some forms of device, it has been proposed that the aqueous solution of the medicament or other active ingredient be discharged through a fine orifice nozzle to form the spray using mechanical pressurizing means, for example using a compressed spring to drive a piston in a cylinder containing the fluid; in others, a pressurized gas is used as the propellant. For convenience the term pressurizing means will be used herein to denote all means by which the pressure required to dispense the fluid is generated and includes mechanical and pressurized gas operated means.
Where very small nozzle apertures, for example those having a diameter of 10 micrometers or less, are used to form fine droplets sizes, it is important to ensure that such small orifice apertures do not become blocked. It has therefore been proposed to provide a filter in the fluid discharge line upstream of the nozzle aperture. Small dimension filters are available, and these typically comprise a mesh or gauze which has a mesh aperture size as low as 3 micrometers or less. However, such filters are flimsy and therefore require some support means to prevent rupturing under the large pressures generated by the pressurizing means. Furthermore, such filters and their support means are additional and often expensive components.
There is, therefore, a continuing requirement for an effective and reliable filter capable of filtering fluid stream down to a very small particle sizes. In spray generating devices, there is usually also a requirement for a non-return valve positioned between the pressurizing means and the atomizing nozzle orifice so as to reduce the risk of residual fluid in the nozzle assembly draining back into the pressurization chamber and contaminating fluid held in a reservoir in the device.
We have devised a form of nozzle assembly incorporating a non-return valve assembly which provides a simple and effective means for reducing the risk of drain back of fluid from the nozzle assembly and may also be used to provide the functions of a filter and/or a filter gauze support in the nozzle assembly.